The broad objective of this project is to understand the structure, function and physiology of the glycoprotein hormones: thyrotropin, luteinizing hormone, follicle stimulating hormone, and chorionic gonadotropin. Recent research developments concerning chorionic gonadotropin include the following: establishment of the renal clearance rates of the subunits of the hormone, characterization of a discrete fragment which is a unique degradation product, demonstration of an estrogen-induced decrease in the testis glycoprotein receptor number and elucidation of the interaction of chorionic gonadotropin with the human thyroid by the classical glycoprotein receptor mechanism. Further refinement of the methodology for the measurement of serum thyrotropin has provided a significant extension of the clinical utility of this test. Future work will continue to focus on improving clinical methodology for the measurement of the glycoprotein hormones and the products of their metabolism, and will give more emphasis to structure-function relationships pertaining to the thyrotropin receptor.